Observations on Factors Influencing the Evaporation of Soil Moisture

Abstract

Important variables which influence the rate of evaporation of soil moisture are (1) the vapor pressure difference between the layer from which water is evaporating and that of the turbulent atmosphere and (2) the resistance to vapor flow of the intervening layer. The vapor pressure difference is associated with the temperature of the layer from which evaporation is taking place and the temperature and relative humidity (vapor pressure) of the turbulent air. While capillarity moves water fast enough to keep the surface moist, the principal resistance to vapor flow is caused by the thin layer of nonturbulent air adjacent to the surface. Resistance increases rapidly as the surface dries so that water vapor moves through a thickening layer of dry soil. Adsorption of moisture by the dry layer and re‐evaporation associated with the diurnal temperature cycle complicate the process. Mositure movement in the upper layers of soil during the evaporation cycle was studied by periodic weighing of soil in vertically stacked porous bottomed containers and through the use of tensiometers. The data show the highly dynamic nature of the moisture regime in the surface layers of soil associated with diurnal temperature changes and the evaporation cycle.

The effect of shrub canopy upon surface temperatures and evaporation in the Negev Desert

“…Our results indicate that the barren intershrub areas first experienced desiccation, which proceeds from the intershrub areas towards the shrub under canopy. It therefore implies that evaporation, rather than transpiration, may be the prime factor controlling the soil water loss in the desert, in agreement with other findings (Hide, 1954;Evans et al, 1981). Since evaporation proceeds from the soil surface inward (Hide, 1954;Van Bavel and Hillel, 1976;Monteith, 1981), it implies that higher moisture content for longer time should be also expected at the under-canopy habitat at depth, just below the evaporative soil layer.…”

“…The differences recorded were higher than these recorded under blue grass in Kansas (Hide, 1954), under coffee plants in tropical Mexico (Barradas and Fanjul, 1986) and under an apple tree in Britain (Davenport, 1967b), where the evaporation rates at the exposed habitat were by 28, 40 and 30-50 per cent higher, respectively. Protected from direct sun and wind, shrubs may ameliorate their under-canopy habitat, thereby responsible for longer wetness duration following rain and for high relative humidity.…”

“…At least as far as annual density Table II A rough estimate of the near-surface vapour pressure and relative humidity at the exposed (EXP) and under-canopy (UC) habitats based on atmospheric and soil data. Atmospheric data were taken from a weather station 7 km south-east of the research site Figure 6) the relative humidity is 100 per cent (see Hide, 1954;Monteith, 1981). d Assuming that e a at the exposed near-surface habitat equals that of the atmosphere.…”

The Effect of Various Supplementary Irrigation Treatments on Plant and Soil Moisture Relationships in a Vineyard (Vitis Vinif era var. Chenin Blanc)

“…Several authors recognized different stages during the drying process (Hide, 1954;Vershinin et al, 1966;Hillel, 1971). Hillel (1971) recognizes two fairly distinct stages when a bare soil dries, viz.…”

Influence of Surface Soil Conditions on Drying in Early Spring

“…The general conditions of evapoiation of water from soil surfaces ale known (Hide 1954;Hanks et al L961. ;Tanner 1957).…”